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Periodic Properties of the Elements

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Periodic Properties of the Elements Periodic Properties of the Elements Review Questions 8.1 A periodic property is one that is predictable based on the element's position within the periodic table. 8.2 The relative size of the sodium and potassium ions is important to nerve signal transmission. The pumps and channels within cell membranes are so sensitive that they can distinguish between the sizes of these two ions and selectively allow only one or the other to pass. The movement of ions is the basis for the transmission of nerve signals in the brain and throughout the body. 8.3 The first attempt to organize the elements according to similarities in their properties was made by the German chemist Johann Dobereiner. He grouped elements into triads; three ele- ments with similar properties. A more complex approach was attempted by the English chemist John Newlands. He organized elements into octaves, analogous to musical notes. When arranged this way, the properties of every eighth element were similar. The modern periodic table is credited primarily to the Russian chemist Dmitri Mendeleev. Mendeleev's table is based on the periodic law, which states that when elements are arranged in order of increasing mass, their properties recur periodically. Mendeleev arranged the ele- ments in a table in which mass increased from left to right and elements with similar proper- ties fell in the same columns. 8.5 Meyer proposed an organization of the known elements based on some periodic properties. Moseley listed elements according to the atomic number rather than atomic mass. This resolved the problems in Mendeleev's table where an increase in atomic mass did not corre- late with similar properties. 8.6 The periodic law was based on the observations that the properties of elements recur and cer- tain elements have similar properties. The theory that explains the existence of the periodic law is quantum-mechanical theory. Electron spin is a fundamental property of electrons. It is more correctly expressed as saying the electron has inherent angular momentum. The value ms is the spin quantum number. An electron with ms = +1/2 has a spin opposite of an electron with ms = - 1/2. 8.8 In the Stern-Gerlach experiment a beam of silver atoms is split into two separate trajectories by a magnet. The spin of the electrons within the atoms creates a tiny magnetic field that inter- acts with the external field. One spin orientation causes the deflection of the beam in one direction, while the other orientation causes a deflection in the opposite direction. Since there were only two trajectories, the spin of the electron is quantized, that is, it can have one of two values and nothing in between. 8.9 An electron configuration shows the particular orbitals that are occupied by electrons in an atom. Some examples are H = Is1, He = Is2, and Li = Is22sj. 263 268 Chapter 8 Periodic Properties of the Elements 8.41 (a) The reactions of the alkali metals with halogens result in the formation of metal halides. 2 M(s) + X2 -» 2 MX(s) (b) Alkali metals react with water to form the dissolved alkali metal ion, the hydroxide ion, and hydro- gen gas. + 2 M(s) + 2 H2O(1) -» 2 M (aq) + 2 OH ~ (aq) + H2(g) 8.42 All of the halogens are powerful oxidizing agents. (a) The halogens react with metals to form metal halides. 2 M(s) + n X2 -> 2 MXn(s) (b) The halogens react with hydrogen to form hydrogen halides. H2(g) + X2-»2HX(g) (c) The halogens react with each other to form interhalogen compounds. e.g. Br2(l) + F2(g) -+ 2 BrF(g) Problems by Topic ctron Configurations (a) Si Silicon has 14 electrons. Distribute two of these into the Is orbital, two into the 2s orbital, six into the 2p orbital, two into the 3s orbital, and two into the 3p orbital. Is22s22p63s23p2 (b) O Oxygen has 8 electrons. Distribute two of these into the Is orbital, two into the 2s orbital, and four into the 2p orbital. Is22s22p4 (c) K Potassium has 19 electrons. Distribute two of these into the Is orbital, two into the 2s orbital, six into the 2p orbital, two into the 3s orbital, six into the 3p orbital, and one into the 4s orbital. Is22s22p63s23p64s1 (d) Ne Neon has 10 electrons. Distribute two of these into the Is orbital, two into the 2s orbital, and six into the 2p orbital. Is22s22p6 8.44 (a) C Carbon has 6 electrons. Distribute two of these into the Is orbital, two into the 2s orbital, and two into the 2p orbital. Is22s22p2 (b) P Phosphorus has 15 electrons. Distribute two of these into the Is orbital, two into the 2s orbital, six into the 2p orbital, two into the 3s orbital, and three into the 3p orbital. Is22s22p63s23p3 (c) Ar Argon has 18 electrons. Distribute two of these into the Is orbital, two into the 2s orbital, six into the 2p orbital, two into the 3s orbital, and six into the 3p orbital. Is22s22p63s23p6 (d) Na Sodium has 11 electrons. Distribute two of these into the Is orbital, two into the 2s orbital, six into the 2p orbital, and one into the 3s orbital. Is22s22p63s1 (a) N Nitrogen has 7 electrons and has the electron configuration Is22s22p3. Draw a box for each orbital, putting the lowest energy orbital (Is) on the far left and proceeding to orbitals of higher energy to the right. Distribute the 7 electrons into the boxes representing the orbitals, allowing a maximum of two electrons per orbital and remembering Hund's rule. You can see from the diagram that nitrogen has 3 unpaired electrons. rm im T I t I T Is 2s (b) F Fluorine has 9 electrons and has the electron configuration Is22s22p5. Draw a box for each orbital, putting the lowest energy orbital (Is) on the far left and proceeding to orbitals of higher energy to the right. Distribute the 9 electrons into the boxes representing the orbitals, Chapter 8 Periodic Properties of the Elements 269 allowing a maximum of two electrons per orbital and remembering Hund's rule. You can see from the diagram that fluorine has 1 unpaired electron. rm QTJ UTUTI 11 Is 2s 2p (c) Mg Magnesium has 12 electrons and has the electron configuration Is22s22p63s2. Draw a box for each orbital, putting the lowest energy orbital (Is) on the far left and proceeding to orbitals of higher energy to the right. Distribute the 12 electrons into the boxes representing the orbitals, allowing a maximum of two electrons per orbital and remembering Hund's rule. You can see from the diagram that magnesium has no unpaired electrons. GLD QTJ ummti dD Is 2s 2p 3s (d) Al Aluminum has 13 electrons and has the electron configuration Is22s22p63s23p1. Draw a box for each orbital, putting the lowest energy orbital (Is) on the far left and proceeding to orbitals of higher energy to the right. Distribute the 13 electrons into the boxes representing the orbitals, allowing a maximum of two electrons per orbital and remembering Hund's rule. You can see from the diagram that aluminum has 1 unpaired electron. DJQ UQ UTUTUTI QTJ I T I I I Is 2s 2p 3s 3p 8.46 (a) S Sulfur has 16 electrons and has the electron configuration Is22s22p63s23p4. Draw a box for each orbital, putting the lowest energy orbital (Is) on the far left and proceeding to orbitals of higher energy to the right. Distribute the 16 electrons into the boxes representing the orbitals, allowing a maximum of two electrons per orbital and remembering Hund's rule. You can see from the diagram that sulfur has 2 unpaired electrons. Dffl GOD UTUTUTI QT] UTI T I T I Is 2s 2p 3s 3p (b) Ca Calcium has 20 electrons and has the electron configuration Is22s22p63s23/?64s2. Draw a box for each orbital, putting the lowest energy orbital (Is) on the far left and proceeding to orbitals of higher energy to the right. Distribute the 20 electrons into the boxes representing the orbitals, allowing a maximum of two electrons per orbital and remembering Hund's rule. You can see from the diagram that nitrogen has no unpaired electrons. RT1 RT1 UTUTUTI QT] UTUTUTI flTI Is 2s 2p 3s 3p 4s (c) Ne Neon has 10 electrons and has the electron configuration Is22s22p6. Draw a box for each orbital, putting the lowest energy orbital (Is) on the far left and proceeding to orbitals of higher energy to the right. Distribute the 10 electrons into the boxes representing the orbitals, allowing a maximum of two electrons per orbital and remembering Hund's rule. You can see from the diagram that neon has no unpaired electrons. UTI RT1 UTUTUTI Is 2s 2p (d) He Helium has 2 electrons and has the electron configuration Is2. Draw a box for each orbital, putting the lowest energy orbital (Is) on the far left and proceeding to orbitals of higher energy to the right. Distribute the 2 electrons into the boxes representing the orbitals, allow- ing a maximum of two electrons per orbital and remembering Hund's rule. You can see from the diagram that helium has no unpaired electrons. Is 8.47 (a) P The atomic number of P is 15. The noble gas that precedes P in the periodic table is neon, so the inner electron configuration is [Ne]. Obtain the outer electron configuration by tracing the elements between Ne and P and assigning electrons to the appropriate orbitals. Begin with [Ne]. Because P is in row 3, add two 3s electrons.
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